Speed control mechanism



FIG. 1 is a side elevation view taken from the right of a speed control mechanism embodying my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a rear elevation view thereof;

FIG. 5 is a front elevation view thereof; and

FIG. 6 is a side elevation view thereof taken from the left of FIG. 5. _ 

The ornamental design for a speed control mechanism, as shown and described. 